1. Field of the Invention
This invention relates to client-server communications. More particularly, this invention relates to reduction in network traffic in the management of locks on server-based resources.
2. Description of the Related Art
TABLE 1Acronyms and AbbreviationsCIFSCommon Internet File SystemFTPFile Transfer ProtocolHTTPHypertext Transfer ProtocolHTTPSHyperText Transfer Protocol Secure socketsLANLocal Area NetworkNFSNetwork File SystemNLMNetwork Lock ManagerOSIOpen System InterconnectionURLUniform Resource LocatorVFNVirtual File NetworkVPNVirtual Private NetworkWAASWide Area Application ServicesWAEWide Area Application EngineWANWide Area Network
Geographically dispersed enterprises often deploy distributed computer systems in order to enable information sharing throughout the enterprise. Such distributed systems generally comprise a number of local area networks (LANS) that are connected into one or more wide area networks (WANs). Enterprises have commonly used dedicated leased lines or permanent virtual circuits, such as frame relay links, to connect their LAN and WAN end-points. While providing generally predictable bandwidth and quality of service, such interconnections are often expensive and represent fixed costs for an enterprise. In addition, when interconnecting over wide areas, inherent latency is introduced in the network, regardless of the bandwidth. More recently, with the development of the Internet, many enterprises use virtual private networks (VPNs) operating over the public Internet, at least for a portion of their data traffic. Although VPNs are typically less expensive than dedicated lines, bandwidth and latency are often unpredictable, particularly when transmitting large files over long distances.
Many LANs include one or more dedicated file servers that receive data from other computers on the LAN via the network for storage on the file servers' hard disks, and supply data from the file servers' hard disks to the other processors via the network. Data stored on file servers is often accessed using a distributed file system, e.g., Network File System (NFS), primarily used for UNIX clients, or Common Internet File System (CIFS), primarily used for Windows clients.
While such networked arrangements are convenient for sharing of information among users throughout the enterprise, there is a significant disadvantage in that software applications that access data resources are primarily designed to access the data resources over a relatively high-speed LAN. Usually, significant latency and performance degradation are observed when a software application accesses a data resource that is located across the WAN in a remote LAN. In a typical example, an enterprise user in a branch office uses a word-processing application to access and modify files. Usually, operations on files that are in the LAN local to the user are relatively quick, while operations on files that are located across the WAN are relatively slow and sometimes unreliable.
The NFS Version 4 protocol implements leases for locks. This feature is described by Pawlowski et al., in “The NFS Version 4 protocol,” published at the System Administration and Networking (SANE) Conference (May 22-25, 2000 MECC, Maastricht, The Netherlands), which is incorporated herein by reference. This paper is available at, the URL “www.nluug.nl/events/sane2000/papers/pawlowski.pdf”. Leases or token-based state management also exists in several other distributed file systems.